The present invention relates to a thermally insulated container. In particular, but not exclusively, the invention relates to a transit container for transporting temperature sensitive items, that is equipped with xe2x80x9carea-under-the curvexe2x80x9d technology.
Thermally insulated containers are used to transport items that are sensitive to temperature and must therefore be maintained within predetermined temperature ranges. Such items include goods such as vaccines and drugs, human organs for transplant, tissue cultures, chilled and frozen foods and many other products, some of which have an extremely high value and are very sensitive to temperature changes. It is essential that such products are maintained within the appropriate temperature ranges during transportation.
This can, however, be a difficult task. Although such goods are normally transported within highly insulated containers, sometimes with hot or cold xe2x80x9cdogsxe2x80x9d (heat reservoirs) to provide additional heating or cooling, heat will still flow into or out of the container, according to the difference between the ambient temperature and the internal temperature of the container. It cannot always be predicted what temperatures will be experienced or how long they will last. If the container is exposed to excessively high or low temperatures for extended periods, the internal temperature may go outside the required range, causing damage to the contents.
A further problem arises in relation to certain live products, such as tissue cultures (for example artificial skin grafts) that are sustained on a nutrient-containing agar. Such products have to be maintained within a fairly narrow temperature range (typically 21-30C) to survive. However, the rate at which they consume the nutrients in the agar also depends on the temperature, increasing as the temperature rises. Therefore, if the temperature remains at the upper end of the acceptable range, the nutrients will be consumed more quickly than if it is at the lower end of that range. In fact, the nutrients may last twice as long at 21C than at 30C. Thus, for maximum life it is desirable to maintain the temperature as close as possible to the bottom end of the acceptable range, while always staying within that range.
A similar problem arises in relation to certain vaccines which degrade at a rate that depends on ambient temperature. As the rate of degradation increases with temperature. It is desirable to maintain the temperature as close as possible to the bottom end of the acceptable range (e.g. 2xc2x0 C.-4xc2x0 C.), while always staying within that range. In this way, the rate of degradation can be minimised.
Another problem with existing insulated containers is that they are generally extremely bulky and not reusable. Their use is not therefore environmentally sound and can lead to major storage and waste disposal problems.
One solution to this problem is of course to use a container that has a built in refrigeration or heating system that is operated by a thermostat to maintain the required internal temperature. However, running a refrigeration or heating system requires a large input of energy and generally such containers are only suitable for use where there is an external power supply They therefore require specialised handling and are not suitable for delivery by normal freight services or for delivering relatively small quantities of goods, such as drugs or vaccines to doctors.
GB2331938 describes a refrigerated container that uses a solid-state Peltier-effect thermoelectric nodule for cooling/heating which is controlled by solid-state temperature-sensing and control modules.
It is an object of the present invention to provide an insulated container that mitigates at least some of the aforementioned disadvantages.
According to the present invention there is provided a thermally insulated container including a payload volume that, in use is to be maintained within a predetermined temperature range it least one heat reservoir and a control device for controlling the flow of heat between the payload volume and the heat reservoir so as to maintain the temperature in the payload volume within the predetermined range.
The heat reservoir may be either hotter than the predetermined temperature range to serve as either a heat source compensating for heat lost to the surroundings or cooler than the predetermined temperature range to serve as a heat sink compensating for heat gained from the surroundings.
The Container automatically compensates for unexpected variations in the ambient temperature ensuring that the contents are maintained at the correct temperature. As it is entirely self-contained, an external power source is not required, allowing it to be delivered by normal delivery services. Nor is a large internal energy supply required, since the container is extremely well insulated to minimise heat transfer, and the heat reservoir or reservoirs have sufficient heat capacity to maintain the products at the required temperature for a considerable time.
Advantageously, the control device includes an external temperature sensor for measuring the ambient temperature. Advantageously, the control device includes an internal temperature sensor for measuring the temperature in the payload volume. Advantageously, the control device extrapolates for the measured temperature or temperatures the rate of transfer of heat to or from the container. By measuring the external and/or internal temperatures, the amount of heating/cooling required can be calculated. Preferably, the amount of heat transferred to and from the box is integrated over time, so that the heating/cooling capacity of the heat reservoir is used only when required. We refer to this as xe2x80x9carea-under-the-curvexe2x80x9d technology.
Advantageously, the control device includes a thermoelectric device for controlling the flow of heat between the payload volume and the heat reservoir. The thermoelectric device may, for example, be a Peltier cell. Alternatively, a mechanical or electro-mechanical device may be used.
Advantageously, the heat reservoir includes a substance that changes state during use to liberate or absorb heat, thereby utilising the large latent heat capacity of the substance.
Advantageously, the heat reservoir includes a first substance for absorbing heat during use from the payload volume, and a second substance that liberates heat during use to the payload volume, so allowing for both heating and cooling as required.
Advantageously, the heat reservoir includes a first substance that changes state during use to liberate heat, and a second substance that chances state during use to absorb heat.
Advantageously, the control device is arranged to bias the temperature in the payload volume towards the lower end of the predetermined range, so maximising the lifetime of products such as live cultures that are sustained by a nutrient-containing agar, or temperature-sensitive vaccines.
Advantageously, the container includes a recording device for recording the temperature in the payload volume, thereby providing means for checking that the contents of the container have been maintained at the required temperature. The recording device may be arranged to calculate from the recorded temperature the remaining lifetime of products transported in the payload volume.
Advantageously, the container has the form of a sealable, thermally insulated box. Advantageously, the box is reusable, thereby reducing waste and alleviating storage problems, and may be substantially transparent to x-rays in at least one direction.